Abstract

A photonic nanocavity with a high Q factor of 100,000 and a modal
volume V of 0.71 cubic wavelengths, is demonstrated. According to
the cavity design rule that we discovered recently, we further improve a point-defect
cavity in a two-dimensional (2D) photonic crystal (PC) slab, where the arrangement of
six air holes near the cavity edges is fine-tuned. We demonstrate that the measured
Q factor for the designed cavity increases by a factor of 20
relative to that for a cavity without displaced air holes, while the calculated modal
volume remains almost constant.

Figures (8)

(a) Schematic of the point-defect nanocavity in a 2D photonic crystal (PC) slab.
The base cavity structure is composed of three missing air holes in a line. The PC
structure has a triangular lattice of air holes with lattice constant
a. The thickness of the slab and the radius of the air holes
are 0.6a and 0.29a, respectively. (b)The
designed cavity structure created by displacing two air holes at both edges in
order to obtain high-Q factor (see Ref. 13). (c) The designed
cavity structure created by fine-tuning the positions of six air holes near both
edges to obtain an even higher Q factor.

(a) The electric field distribution (Ey) of the fundamental mode for a cavity without air hole displacement
at both edges. (b) The profile of (a) along the center line of the cavity and
the fitted curve corresponding to the product of a fundamental sinusoidal wave
and a Gaussian envelope function. (c) The 1D FT spectra of (b). The leaky
region or light cone is indicated by the gray area. (d), (e), (f) The electric
field distribution (Ey), the Ey profile at the center line and the fitted curve, and the 1D FT
spectra, respectively, for the cavity structure shown in Fig. 1(b). The displacement of air holes at the edges is
set at 0.20a. (g), (h) The 2D FT spectra of (a) and (d),
respectively. (i), (j) The 2D FT spectra of Ex for cavities of (a) and (d), respectively.

(a) Cavity Q factors and the modal volume (V)
obtained theoretically for cavities with a range of displacements of air holes
at position A (the nearest neighbors). (b) Those for cavities with a range of
displacements of air holes at position B (the second nearest neighbors), whilst
fixing the position of air holes A at their optimum value of
0.200a. (c) Those for the cavities with a range of
displacements of air holes at position C (the third nearest neighbors), whilst
fixing the positions of air holes A and B at their optimum values of
0.200a and 0.025a, respectively.

SEM images of one of the fabricated samples, including the point-defect cavity
with displaced air holes A, B, and C. (a) Magnified view of the point-defect
cavity. (b) Top view of the sample. A line-defect waveguide was introduced near
the point-defect cavity.

(a) Cavity Q factors (Qv) obtained
experimentally for cavities with various displacements of air holes at position
A. (b) Those for cavities with various displacements of air holes at position
B, whilst fixing the position of air holes A at their optimum value of around
0.176a. (c) Those for the cavities with various
displacements of air holes at position C, whilst fixing the positions of air
holes A and B at their optimum values of around 0.176a and
0.024a, respectively.